Effect of Alkali Metal Dissolution from Feldspathoid on AAR Expansion

To investigate the effect of alkali dissolution from aggregates on ASR expansion, alkali metal-rich nepheline syenite powder (NS) was substituted as a fine aggregate replacement in reactive chart aggregate concrete and its expansion behavior was evaluated by concrete prism tests with alkaline wrapping. The results showed that the addition of 5wt% NS had no effect in the short ages but promoted expansion in the long ages. The effect in terms of total alkali content was an increase of 1.75 kg/m3, while the RILEM AAR-8 evaluation resulted in an alkali metal increase of 0.18 kg/m3, which was an underestimate. This may be due to too little Ca(OH)2 added in the test procedure of RILEM AAR-8. As the gradual dissolution of alkali metals from the NS, and the alkali silica gel produced slowly, contributes efficiently to the expansion, suggesting that expansion may continue over the long term in low total alkali content and low temperature environments, when alkali dissolving minerals are present.